Lubricating oils for gasoline-fueled internal combustion engines are usually formulated with a number of additives for enhancing their performance in service. In order to reduce corrosive engine wear due to the attack by acids resulting from incomplete fuel combustion or oil deterioration, engine lubricants generally contain additives which are alkaline materials. Among the principal additives are overbased sulfonate and phenate salts of alkaline earth metals. Commercially available additive concentrates generally comprise colloidal suspensions of calcium or magnesuim carbonate in an oil solution of calcium sulfonate having long non-polar chains. These overbased materials are stable dispersions with a maximum particle size of 100 angstroms. However, calcium carbonate particles are undesirably abrasive.
Recent interest in the development of methanol-fueled passenger vehicles has shown that currently available lubricating oil systems are not adequate for lubrication of methanol-fueled spark ignition engines. Formic acid generated by the incomplete combustion of methanol fuel may cause excessive piston ring and cylinder bore wear on engines operating at low temperatures. Although methanol-fueled engine development has continued with existing lubricating oils, the need for more effective lubricants has lately become very clear.